Electron tube amplification system



B. F. LEE

ELECTRON TUBE AMPLIFICATION SYSTEM Filed April 25, 1928 July 5, 1932.

IN VEN TOR.

2224'22 Flee,

Patented July 5, 1932 PATENT OFFICE BENJAMIN F. LEE, OF SPRAY, NORTH CAROLINA VELECTRON TUBE VAMIPLIFICATION sYsTEm:

Application filed April 25,

My invention relates broadly to electron tube amplification systems and more particularly to a coupling circuit for the input and output systems of electron tubes connected for amplification of energy at high frequencies.

One of the objects of my invention is to providea high frequency coupling system between the output circuit of one electron tube and the input circuit of a succeeding electron tube whereby the maximum voltage may be impressed upon the grid of the succeeding tube from the output circuit of the preceding tube and the impedance of the output circuit made equal to the internal'impedance of the electron tube. 4

Another object of my invention is to provide a coupling system for stages of electron tube amplification including an inductance extending between the plate electrode of one stage of amplification and the grid electrode of the succeeding stage of amplification where a tapped connection is taken from a nodal point in the inductance to the filament side of the amplifier system for impressing all of the potential developed across the inductance upon the input circuit of the sucoeeding tube.

A further object of my invention is to provide a coupling circuit for cascaded electron tubes in which a resonance wave coil is disposed between the plate electrode of one tube and the'grid electrode of a succeeding tube and the coil electrically balanced to establish a nodal point intermediate the ends with a connection taken from the nodal point to the filament circuit of the electron tubes for transferring the maximum amount of energy 40 from the output circuit of one tube to the input circuit of the succeeding tube.

A still further object of my invention is to provide a circuit arrangement for a cascade electron tube amplifier system wherein high frequency energy is transferred through a conductively connected circuit from the output system of one electron tube to the input system of the succeeding electron tube, with a circuit for controlling the biasing potential 0 of the succeeding electron tube connected 1928. Serial No. 272,766.

with a nodal point in the conductively connected circuit.

My invention will be more fully understood from the specification hereinafter following by reference to the accompanying drawing in 55 which:

Figure 1 diagrammatically illustrates one embodiment of the circuit arrangement of my invention; Fig. 2 illustrates a modified form of circuit arrangement of the invention; and Fig. 3 shows a still further modification of the circuit of my invention.

My invention is directed to improvements incascadeamplification systems for use with radio receiving andtransmitting apparatus and is particularly suitable in circuits of high frequencies;

In operating a vacuum tube as an amplifier, there are two conditions that have to be 4 complied with to enable the tube to be oper- 7o ated most efficiently, viz: (1) The highest possible voltage should be impressed on the grid of the tube, and (2) the external impedance of the plate circuit should equal the internal plate impedance of the tube.

In employing vacuum tubes in a cascade amplifier circuit, some form of coupling has to be used to transfer the voltage or power developed in the plate circuit of one tube to grid of the adjacent tube. There are tWo methods of coupling vacuum tubes used in the art at the present time, viz: (1) Transformer coupling; (2) impedance coupling.

- Transformer coupling works most efficiently at low and moderate frequencies, and is very extensively used in practice; but the transformer method is not suitable for use at the higher frequencies. The same may be said of the impedance method of coupling, because in using this method of coupling, a blocking condenser and grid leak are necessary. The object of the blocking condenser is to keep the positive B voltage of the plate from the grid of the tube to which the tube is coupled; Since thisblocking condenser is in the grid circuit a path must be provided from the grid of the tube to its filament to prevent the tube becoming inoperative because of the accumulation of electrons on the grid of the tube. This is usually in the form of a high non-inductive resistance connected from grid to the filament of the tube. Now, it is well known that a non-inductive resistance does not offer much resistance to high frequency currents, consequently, the impedance of the grid leak at such frequencies would not be high enough for most efficlent operation, thus failing to fulfill condition (1) viz: That the highest possible voltage be impressed on the grid of the tube. Furthermore, in the usual coupled circuit an inductance and resistance are disposed in parallel and form the load for the plate circuit of the tube. Since two or more circuits in parallel have less resistance than the same circuits in series, the impedance of the plate circuit of such coupled systems is therefore comparatively low. Therefore such coupling methods do not fulfill condition (2) viz The external impedance of the plate circuit should equal the internal plate impedance of the tube.

In the coupling system of my invention I provide a resonance wave coil in series between the plate electrode of one electron tube and the grid electrode of a succeeding electron tube and impress upon the resonance wave coil the energy amplified by one electron tube for transfer to the input circuit of the succeeding electron tube. In order to impress the required biasing potential on the grid of the succeeding electron tube I select a point of zero potential in the resonance wave coil and introduce the required potential at that point in a manner which tends to eliminate losses in the coupling system.

In the radio frequency amplification system of my invention the circuits are tuned to secure maximum selectivity and the maximum impedance that can be inserted in the tuned circuit is the impedance of the tuning coil at resonance. Therefore, by putting the tuning coil and grid-filament circuit of the coupled tube in series in the plate circuit of the amplifying tube condition (2) is fulfilled, viz: The external impedance of the plate circuit should equal the internal plate impedance of the tube. Also since there is no grid leak to shunt any of the high frequencies around the grid-filament circuit, the full voltage is developed by the resonance coil and impressed on the grid of the tube, thus fulfilling condition (1), viz: The highest possiligle voltage be impressed on the grid of the tu e.

Referring to the drawing in more detail the amplification system of my invention is shown connected to an antenna ground system 17 including. electron tubes 1, 2 and 3. A tuned circuit 4.6 is employed for coupling the antenna ground system to the input of the radio frequency amplifier. Each electron tube contains filament, grid and plate electrodes which I have designated by subscripts la, 1?), 10, and 2a, 2b and 20, and 3a 3b and 3c. The output circuit of the electron tube 1 includes reactance 8 and high potential source 9. A connection is estab lished with the input circuit of the succeeding electron tube 2 through blocking condenser 11 and resonance wave coil 12. A condenser 15 is connected across the terminals of the resonance Wave coil 12 and serves to tune the resonance wave coil. The opposite terminal of the resonance wave coil 12 connects to the grid 2!). The resonance wave coil transfers the energy from the output circuit of electron tube 1 to the input circuit of electron tube 2. In order to secure the proper biasing potential on the grid of electron tube 2 a connect-ion is taken from the negative side of the source of potential shown at 16 and connected at 14 to a nodal point along the resonance wave coil. A high resistance leak path 17 may be provided across the source of potential 16. The output circuit of electron tube 2 includes reactance 18 and high potential source 19. The output circuit connects through blocking condenser 20 and resonance wave coil 22 with the input circuit of detector tube 3 through a grid leak and grid condenser 25. A condenser 21 is connected across the terminals of the resonance wave coil 22 and serves to tune the resonance wave coil. A high resistance leak path 2A connects at 23 which is a nodal point along the resistance path with the positive side of the filament heated by a source designated at 10, and the output circuit of electron tube 3 includes sound reproducers 6, such as a telephone headset or loud speaker and high potential battery 27.

In Fig. 2 I have shown a coupling system wherein the resonance wave coil in each coupling circuit is divided into two parts axially aligned end to end. In Fig. 1 the resonance wave coil has been illustrated as one continuous inductance having a zero point of potential at its center. In Fig. 2 the same zero potential point in the resonance wave coil exists and the coil has been severed at the zero point with the portions thereof disposed in the same axial alignment and the end of the portion 28 of the resonance wave coil connected to the positive side of the high potential source 9. The severed end of the portion 29 of the resonance wave coil connects to the filament 2a through the conductor 42. Inasmuch as the connections are made at the point of zero potential there will be no tendency for the radio frequency currents to pass from c to e or from a to I). Where no radio frequency currents flow from the plate electrode 10 through the portion of inductance 28 to point 0 through the battery 9 to point e the coil system 28-29 will not function as a transformer but will function as an impedance coil. Condenser 31 acts as a balancing condenser to accurately locate the point of zero potential of coil system 2829 when tuned to resonance by condenser 15.

A path for the plate current of electron tube 1 is provided through the inductance coil 28 and the impedance 8 and 18 illustrated in Fig. 1 can thus be eliminated as well as blocking condensers 11 and 20. The condenser 30 in Fig. 2 operates to prevent the impression of positive potential from battery 9 upon the grid of the succeeding tube and also functions as a balancing condenser to locate the point of zero potential in coil system 28-29 in the same manner as condenser 31 functions. The output circuit of the electron tube 2 connects to the input circuit of electron tube 3 through a similar coupling system which includes portions of the resonance wave coil at 32 and 33 connected with balancing condensers 34: and 35, which function in a manner similar to the operation of condensers 30 and 31. The tuning condenser 21 connects across the ends of the resonance wave coil system 3233 and operates in a manner similar to condenser 15. A high resistance 24 extends from a connection to one end of the portion of the wave coil 33 through the positive side of the filament heating source 10.

In Fig. 3 I have shown means for more accurately fixing the Zero potential point in the resonance wave coil 12 by means of a condenser system having a fixed plate 37 connected to one terminal of the resonance wave coil and the fixed plate 38 connected to the opposite terminal of the wave coil. The center point 14 of the resonance wave coil 12 connects to variable plate 40 and to the source of the biasing potential at 16. The zero potential point may be thus selected in the resonance wave coil and theproper bias introduced through the resonance wave coil at that point through the grid circuit to the grid electrode 2?). The plate potential of electron tube 1 is blocked from the grid circuit of electron tube 2 by means of condenser 11 and passes through impedance 36 to the plate electrode I have found that in the operation of the amplification system of my invention that substantially all of the potential developed in the output circuit of one electron tube may be impressed upon the circuit of a succeeding electron tube. In this way maximum volume of signal energy may be rendered effective to actuate a sound reproducer. The normal capacity of electron tube 2 is in series with the isolated circuit formed by inductance 12 and condenser 15. I am enabled to secure increased amplification by the circuit arrangement described over that amplification heretofore obtainable with a similar number of tubes.

While I have described my invention in certain preferred embodiments, I desire that it be understood that modifications may be made and that no limitations upon my invention are intended other than are imposed by the scope of the appended claims.

What I claim as new and desire to secure by Letters Patent of the United States is as follows:

1. In an electron tube amplification system, a plurality of electron tubes each having grid, cathode and plate electrodes, an in put circuit interconnecting said grid and cathode electrodes, an output circuit interconnecting said plate and cathode electrodes, a resonance wave coil divided into two axial ly aligned sections and interposed between said circuits, one of said sections being connected at one end with the plate electrode of one electron tube and the other of said sections being connected at one end with the electrode of the succeeding tube, and connections between the adjacent ends of said resonance wave coil with the cathode electrodes of each of said tubes.

2. In an electron tube amplification system a plurality of electron tubes each having grid, cathode and plate electrodes, an input circuit connecting the grid electrodes, an output circuit connecting the plate electrodes, a high potential source for energizing the output circuits, a resonance wave coil extending between the high potential source in the output circuit of one tube and the grid electrode in the input circuit of a succeeding electron tube, said resonance wave coil being divided into axially aligned sections and a connection between points of zero potential in each of the sections of said resonance wave coil with the cathode electrodes of said electron tubes.

3. In an electron tube amplification system a plurality of electron tubes each having input and output circuits with the output circuit of one electron tube interlinked with the input circuit of a succeeding electron tube and a resonance wave coil disposed between said circuits, said resonance wave coil being divided into axially aligned separate sections at points of zero potential along the length thereof, and connections extending from the ends of the sections of said resonance wave coil at zero potential to the cathode electrodes of said tubes for efiecting the transfer of energy from one tube to a succeeding tube.

4. In an electron tube amplification system, a plurality of electron tubes each having grid, cathode and plate electrodes, an input circuit interconnecting said grid and cathode electrodes, an output circuit interconnecting said plate and cathode electrodes, a coupling system disposed between said circuits com prising a resonance wave coil consisting of a pair of independent sections with the end of one of said sections connected wit-h the plate electrode of one electron tube and the end of the other section connected to the grid electrode of the succeeding electron tube, sections being axially aligned end to end and a circuit for introducing a biasing potential at a nodal point along'said resonance wave coil atone end of said last mentioned section for fixing the operating potential of the grid of the succeeding electron tube.

5. In an electron tube amplification system, a plurality of electron tubes each having grid,

. cathode and plate electrodes, an input circuit interconnecting said grid and cathode electrodes, an output circuit interconnecting said 1'0 plate and cathode electrodes, a coupling system disposed between said circuits comprising a resonance wave coil, consisting of a pair of separate sections divided at a point of zero potential along the length thereof said sections being axially aligned end to end and a circuit for introducing biasing potential at said point of Zero potential in one of said sections of said resonance wave coil for fixing the operating potential of the grid of one of said electron tubes.

6. In an electron tube amplification system a plurality of electron tubes each having grid, cathode and plate electrodes, an output circuit connecting the plate electrode of one of said electron tubes, an input circuit connecting the grid electrode of a succeeding electron tube, a resonance wave coil disposed between said circuits, said resonance wave coil being divided into a pair of axially aligned longitudinally extending sections at a point of Zero potential along the length thereof and having one end of one of said sections connected to the plate electrode of one electron tube, and the opposite end of the other of said sections connected to the grid electrode of the succeeding electron tube, circuits eX- tending between adjacent ends of said sec tions at points of zero potential in said resonance wave coil and said cathode electrodes, one of said circuits including a source of biasing potential for the grid electrode of said succeeding electron tube and means connected to the opposite ends of said resonance wave coil for adjusting the position of the zero potential point in said resonance wave coil to correspond to the ends of the adjacent sections of said resonance wave coil.

In testimony whereof I afiix my signature.

BENJAMIN F. LEE. 

